Anodes of this type are produced by sintering fine niobium suboxide particles to form a sponge-like structure with an extremely large surface area. A dielectric niobium pentoxide layer is produced on this surface by electrolytic oxidation, and the capacitor cathode, which may consist of manganese dioxide or a polymer electrolyte, is produced on the pentoxide layer. The process used to produce anodes or capacitors of this type, as well as the production of the capacitor precursor powders, includes a range of mechanical and thermal treatment steps in vacuo or reactive and/or protective gas, which entail the risk of contamination with elements which have an adverse effect on the capacitor properties. Therefore, according to WO 02/086923 A2, it is proposed that all equipment used for the mechanical or thermal treatment involved in the production of anodes consist of niobium metal or at least be coated with niobium metal.
One drawback in this context is that niobium metal is a so-called oxygen getter material, which tends to take up oxygen at high temperatures. Accordingly, during high-temperature treatment steps involved in the production of niobium suboxide anodes, which may involve temperatures of up to 1600° C., there is a high risk of oxygen being withdrawn from the niobium suboxide in an uncontrolled way, in particular if there is direct contact between the niobium suboxide and the niobium metal at this high temperature. Furthermore, the niobium metal becomes increasingly brittle as a result of the uptake of oxygen when used repeatedly, and therefore typically has a short service life.